Method of cleaning metals



.Patented Feb. 23, 1932 GRINNELL JONES, OF CAMBRIDGE, MASSACHUSETTS METHOD OF CLEANING EMAILS No Drawing. Original application filed September 7, 1927, Serial No. 218,115. Renewed June 22, 1931.

Divided and this application filed August 24, 1928. Serial No. 391,932.

This invention relates to improvements in metal cleaning and more particularly .to the removal of tarnish from articles of silver.

Hitherto, one of the most widely used methods of cleaning gold or silver articles has been by the use of abrasives, either alone or.

incorporated in a paste or cloth by means of tallow or other grease. Such abrading process is necessarily slow and has the disadvantage of abrading or removing a portion of the metal surface as well as the tarnish. A further disadvantage resides in the fact that it is very ditficult or almost impossible to clean depressed portions of embossed or engraved articles.

Another method in wide use is that of dissolving the tarnish in strong, hot solutions of cyanides. Cyanides, as'is well known, are

extremely poisonous, and cannot be handled with safety in the ordinary household. Further, any carelessness in washing off the cleaned articles after treatment might result in the fatal poisoning of anyone using them. In addition, the well known solvent action of cyanides for silver, in the presence of air, is a factor to be taken into account.

T he most commonly used method is to immerse the article to be cleaned in a boiling alkaline solution, such as a solution of sodium carbonate, sodium bicarbonate or trisodium phosphate, contained in an aluminum pot or like vessel. Ordinary salt may be addedto speed up the electrochemical action. The article to be cleaned must be in electrical contact with the aluminum, either directly or through another piece of metal, so that an electric current can flow from the metal to be cleaned to the aluminum and back to the metal through the electrolyte. This combination forms a short-circuited electrolytic cell in which the'aluminum dissolves electrolytically and the sulfide of the tarnished metal is reduced electrochemically to the metal. The sulfide ion liberated unites with the hydrogen set free to form gaseous hydrogen sulfide. Hydrogen sulfide has an offensive odor. This old method of .cleaning silver leaves the metal with a dull or unpolished surface and injures .the aluminum pot used.

, It is an object of this invention to provide an improved method of cleaning metals,

which method is adapted to remove tarnish and which does not require the articles under 1treatment to be immersed in a cleaning soluion.

It is a further object of this invention to provide such an improved process which will permit the removal of tarnish from metal, together With the simultaneous neutralization of evolved hydrogen sulphide.

I accomplish these and other desirable objects by providing a composition of matter comprising a finely divided metal in combination with a substantially anhydrous acid or acid salt, with or Without a neutral salt, with an anti-odor, and with or without an abrasive, put up either as a powder, or a paste, or mcorpora'ted in a cloth or the like, and adapted to be activated when wet.

In the manufacture of the composition comprising my invention I use a metal which is sufliciently electropositive with respect to the metal to be cleaned as to have a detarnishing action thereon. I have found that to se-v cure the best results the' metal should be finely divided, or pulverized if possible. As the result of protracted experiments, I have found that the following metals are suitable for use in a composition for detarnishing silver or other tarnishable metals or alloys, when taken in conjunction with the acids and acid salts to be hereinafter referred to. The metals, in the order of their reducing power, are: magnesium, zinc, manganese, cadmium, iron and aluminum. It will, of course, be readily understood that other metals having. the desired characteristics may be used, and the foregoing are given merely by way of illustration. The factors of availability of materials, cost, ease of processing grinding, mixing) ,stability, reducing power, and hardness enter into the choice of the particular metal to be used, and such choice will be readily made by those skilled in the art'for any given set of conditions.

In combination with any of the foregoing metals, I make use of a suitable acid or acid salt. As I have mentioned above, the particular acid or acid salt chosen must ily soluble in water, non-poisonous, non-hybe readelectrical conductivity with moderate acidity reaction between the components,

and therefore give rapid detarnishing action without excessive generation of heat.

After numerous experiments, I have found that the following compounds give very satisfactory results in conjunction with the metallic components heretofore described. These compounds are given by way of illustration only, as it will be readily apparent that I may use any compound having like characteristics without departing from the spirit of my invention. The preferred compounds are as follows: citric acid, tartaric acid, benzoic acid, salicylic acid, sodium acid citrate, potassium acid citrate, sodium acid tartrate, potassium acid tartrate and monosodium dihydrogen phosphate.

I have also found that the acid or acid salt may be omitted entirely from the composition in order to avoid any premature reaction between the components. In this case the user can obtain the desired result by adding any appropriate acid solution to the com-v position at the time of use. I find that vinegar, lemon juice, sour milk and like acidulated compositions are suitable for use with the finely divided metals above mentioned.

. These acid materials are available in every household, and are ofrelatively low price.

In preparing my improved composition, I first reduce the individual components to any desired state of subdivision by appropriate mechanical or chemical means. The desired quantity of the separate ingredients is then taken and the whole is intimately mixed in a suitable machine such as a ball mill, or the like. To prevent any undesirable premature I carry out the grinding and mixing operations under substantially dry conditions. After such treatment, the resulting mixture is packaged or otherwise prepared, as will be described more fully hereinafter.

If it is desired to improve the electrical conductivity of the film of liquid on the surface of the metal being cleaned, especially where a weak acid is being used, I add a salt to the above described mixture. I find that practically any cheap, non-poisonous, non- .hydroscopic, easily soluble neutral salt may be used. Sodium chloride is the cheapest and most readily available, although I secure efficient results by the use of any of sodium citrate, sodium tartrate, or sodium sulfate. It will be readily apparent that any salt having the desired characteristics can be made use of in the compositions which I have described.

Where an improved polish is desired, I incorporate an abrasive in the composition. The abrasive selected must be both soft and chemically inert. I refer to use infusorial earth or some other orm of silica, although it is to be understood that any suitable material may be used.

The salt and abrasive, where used, may be incorporated in the mixture during the grinding and mixing operations, or may be added after these steps have been accomplished. In the latter case, a simple mixing will generally sufiice to disperse them thoroughl throughout the mixture.

As have intimated hereinbefore, one of the outstanding disadvantages of the use of compounds suggested for use as cleaners has been the unpleasant odor of the hydrogen sulfide given off during the cleaning or detarnishing process. I overcome this disadvantage by the addition of a metal or metal compound, or any suitable chemical reagent which will react with the hydrogen sulfide as it is formed. Another methodof eliminating the odor of hydrogen sulfide is the addition of a masking perfume such as an essential oil or like odoriferous compounds.

To accomplish the absorption of the hydrogen sulfide I incorporate with the metal-acid composition a small quantity of a substance which is adapted to react with the gas to form an odorless compound and which has no deleterious effect on the surface of the metal under treatment. I have found that the metals or their oxides which form sulfides insoluble in dilute acids, are effective in preventing the escape of hydrogen sulfide, and thus act as an anti-odor. I prefer to use copper oxide in finely divided form, although other metals or their oxides having the desired properties such as lead or bismuth, for instance, can be used;

As mentioned above in the case of the salt and abrasive additions to the mixture, the anti-odor may be ground up with either of the reacting components, or preliminarily ground and added in the mixing stage.

The following are preferred examples of compositions which are suitable for use in the powdered form:

Grams Magnesium 13.2 Sodium acid tartrate 100.0 Copper oxide 3.3 Zinc 33.3 Sodium acid tartrate 100.0 Copper oxide 8.4

In use, the substantially dry, powdered mixture of an electropositive metal, acid or acid salt, with or without any of the neutral salt, anti-odor or abrasive, above mentioned, is sprinkled on a damp cloth and applied to the article to be cleaned. The operation is very easily performed. There are no causcloth upon which sprinkled, the fundamental electrochemical tic alkaline materials or strong acids to corrode the hands of the user there is no boiling up of the electrolyte; and the articles after cleaning merely require'a simple rising in tap water to remove the reagents or they can be wiped with a damp cloth.

As noted previously, the acid or acid salt may be omitted from the composition and any of the materials mentioned (vinegar, lemon juice, sour milk), can be used to dampen the the other ingredients are reactions being unchanged.

The powdered composition can be ackaged in any suitable manner. Care shou d be taken to have the package substantially airtight to prevent access of moisture to the ingredients. For export trade, or for localities which are excessively dam it may be desirable to omit the acid or acid salt from the composition, the user supplying such omission in the manner designated. As examples of suitable forms of packages may be mentioned the cans used for dispensing toothcleaning powders and the hermetically sealed glassine packets or envelopes.

Any of the powder compositions made according to my invention may be incorporated in a suitable Water soluble vehicle to form a paste, and the resulting product put up in jars or collapsible tubes. The vehicle or binder used for carrying the owdered ingredients, prepared as above escribed, is moorporated therewith in any suitable machine, or the ingredients may be wet-ground in the vehicle or binder, care being taken to exclude moisture. As will be readily understood, the

vehicle or binder used for carrying the powdered ingredients should be a non-aqueous, non-ionizing liquid, having a minimum of solvent action on the acid or acid salt used, and be readily miscible with water so that it may work by dilution therewith. I have found that denatured alcohol and lycerine are suitablevehicles, but I wish it to e understood that these are merely illustrative since other materials having the desired characteristics may be used.

Soap has been widely used as a vehicle for carrying'powdered materials which are to be used as abrasives or the like, but I find that it is not suitable for the purpose of my invention. This is due to the fact that the use of soap leaves an infinitely thin saponaceous film on the cleaned metal, which film exerts a deleterious effect on the metal and facilitates further tarnishing.

Where is it desired to impregnate a cloth, paper or like fibrous material with any of the compositions set forth I mix a water soluble gum, such as karachi gum, the metal and a neutral salt With Water and apply the mixture to the cloth in a machine known to the textile industry as a padder. The water is removed from the fabric by evaporation. The acid .sour milk are suitable ch1 gum I may use equivalent materials, such is removed as starch, dextrine or other carbohydrate gums.

As with the powder and the paste modificatlonsv of my invention, the acid or acid salt maybe omitted from the impregnating composltion used in connection with the fabric, and the'latter moistened with an appro priate acidulated solution at the time of use. As already noted, vinegar, lemon juice, or for this purpose. These materials have been given by way of example only, and it is obvious that any suitable fruit juice or the like may be used.

he impregnated fabric can be cut to an suitable size and put up in moisture-proof packages or envelopes.

It will now be appreciated that I have provided a composition which is adapted for use in the detarnishing of metals, and one which obviates the necessity of using compllcated apparatus or chemicals. The slmpllcity of operation, and freedom from odors and mussiness which characterizes the use of the compositions comprised within the spirit and scope of my invention are a distmct advance over the practice of the prior art.

While I have disclosed preferred embodiments of my invention, I Wish it to be understood that these are but preferred embodiments which typify others in which may be incorporated the underlying features of this invention. Modifications may be made in the proportions of the ingredients used, within the spirit and scope of my invention,

and such modifications are intended to becovered by the appended claims.

This application is a division of my application for Metal cleaning compounds, Serial No. 218,115, filed September 7 1927.

I claim:

1. The method of restoring metal surfaces which are tarnished with a metal sulphide, comprising changing the sulphide chemically into undissociated hydrogen sulphide, and continuously removing the hydrogen sulphide formed by causing it to combine with another substance to form a substantially inodorous compound.

2. The method of detarnishing metal surfaces which are tarnished with a deposit of a metallic sulphide, comprising changing the sulphide chemically into undissociated hydrogen sulphide and continuously removing the hydrogen sulphide by bringing it into contact with a metal which will react with the hydrogen sulphide to form a sulphide of such metal.

3. The method of detarnishing metals which are coated with a metallic sulphide,

comprising .convertin the sulphide into hydrogen sulphide an removing the hydrogcn sulphide by causing it-to react in the 5 presence of water with a metal to form an insoluble sulphide.

4. The method of detarnishing metals coated with a metallic sulphide, comprising converting the sulphide to hydrogen sulphide, and then contacting the hydrogen sulphide with copper oxide.

5. The method of detarnishing metals which are coated with a metallic sulphide, comprising treating the sulphide with a reducing metal incorporated in an acidulated vehicle to form hydrogen sulphide, and contacting the hydrogen sulphide with a metal which forms a sulphide insoluble in said acidulated vehicle.

G. The method of detarnishing metals which are coated with a metallic sulphide, con'lprising subjecting the sulphide to the action of a reducing metal incorporated in an acidulated vehicle, and then contacting the evolved hydrogen sulphide with a compound of copper.

7. The method of detarnishing metals which are coated with a metallic sulphide, comprising subjecting the sulphide to the action of a reducin metal incorporated in an acidulated vehicle, and then contacting the evolved hydrogen sulphide with an insoluble compound of copper.

8. The method of cleaning silver, comprising subjecting the coating of tarnish to the action of a suitable reducing metal to form hydrogen sulphide, and then treating the hydrogen sulphide with a precipitant.

9. The improvement in electrolytic metal cleaners, the action of which involvesthe formation of hydrogen sulphide, comprising incorporating in the cleaner a metallic compound which will react with hydrogen sulphide to form an insoluble sulphide.

10. The/improvement in metal cleaners, the action of which involves-the formation of hydrogen sulphide, comprising incorporating in the cleaner a compound of copper.

50 11. The improvement in metal cleaners, the action of which involves the formation of hydrogen sulphide, comprising incorporating cupric oxide in the cleaner.

12. The improvement in metal cleaning which involves the formation of hydrogen sulphide, comprising contacting the hydrogen sulphide with a metal which reacts therewith to form an insoluble sulphide.

6o GRINNELL JONES. 

